It differs from Furcula furcula in its generally larger size, but more especially in the shape of the black line forming the outer margin of the central band; this forms a clean curve whereas, in the alder kitten it is always more or less angled or dentate towards the front margin of the wings.

Seitz - sharper black edges to the median band, which bears an evenly incurved shallow sinus on the distal side to below vein 2; of the exterior dentate lines usually only 2 are well developed.

As in the case of furcula, a northern Scandinavian-Laponian race is distinguished by its dark smoky ground-colour, saltensis Schoyen.

Bdv., in which the markings are leas developed, or some even entirely obsolete, especially in the marginal area.- — fuscinula Steph., arcuata Steph., integra Steph.

Larva similar to that of furcula, with similar dark red-brown dorsal spots; first stage blackish, later ones yellowish green with sparse red lateral dots; the large triangular thoracical patch divided by a narrow pale median line and irregularly variegated with light spots, as well as edged with reddish yellow.